Transport properties of concrete using limestone filler or fly ash as a partial replacement to cement

Abstract

Globally, concrete is the most used material in the construction industry. When used for this purpose, concrete has two main functions, that of taking compressive forces in the structure and that of acting as a protection to the steel reinforcement. Although other materials do exist, steel is by far the most widely used material as reinforcement to concrete. Steel has the limitation of being susceptible to corrosion which would result in a loss of strength. The presence of oxygen and water are needed for this process to occur, whilst the presence of chlorides accelerate the process. In this regard, the capacity of the concrete to restrain the passage, or transport, of these aggressive substances into the concrete leads to a much more durable structural member. The production of cement is a very energy intensive process which is responsible for 7% of the world's CO2 emissions. It is therefore of ever growing importance for suitable substitutes to cement to be investigated. In this study, the effect of a partial replacement of cement with limestone filler or with fly ash is examined with regards to strength performance and transport properties. Different mixes containing 5%, 15%, and 35% limestone filler replacement and 10%, 20%, 30% and 40% fly ash replacement were compared to a control mix keeping a 0.52 water/powder ratio for all mixes. The concrete transport properties were assessed and analysed for the following: water permeability, gas permeability, porosity, chloride permeability and chloride migration.